1. Field of Invention
The present invention relates to an optical fiber connector, a ferrule to be used for the optical fiber connector, and a method for producing the ferrule. In particular, the present invention relates to an optical fiber connector for correctly aligning mutual positions of cores of optical fibers and connecting them to one another by inserting the optical fibers into cylindrical ferrules to support them, a ferrule to be used for the optical fiber connector, and a method for producing the ferrule. The present invention also relates to a wire member-supporting apparatus to be used for producing the ferrule.
2. Description of the Related Art
In recent years, the electric cable for the telephone line is being replaced with the optical fiber cable on a worldwide scale. The use of the optical fiber is not limited to the optical communication based on the telephone. The optical fiber is also widely used for optical devices, apparatuses for LAN, and a variety of optical systems. Methods are known to mutually connect optical fibers in such an optical communication system, including a permanent connection method based on the use of fusion or mechanical splice, and a detachable connection method based on the use of an optical fiber connector. It is required for the optical fiber connector used for the latter method that attachment and detachment can be easily performed, and the optical fiber connector is resistant to the environment. Additionally, in order to respond to the demand for the optical communication system to realize long distance communication and large capacity, for example, it is required for the optical fiber connector that the connection loss is low, and the nonreflective treatment is applied in order to stabilize laser transmission.
Conventionally, as shown in (C) of FIG. 1, an optical fiber connector comprises tubular parts (hereinafter referred to as xe2x80x9cferrulesxe2x80x9d) 1a, 1b having a perfect circular cross section for highly accurately holding optical fibers 40a, 40b having a diameter of about 0.13 mm at predetermined positions and fixing them coaxially, and an aligning section 42 for holding the ferrules 1a, 1b while allowing them to make mutual abutment. For example, the ferrule has a columnar configuration as shown in (A) of FIG. 1, and it is made of a zirconia ceramic material or the like. The ferrule 1 shown in (A) of FIG. 1 is a ferrule of the one-core type. For example, the ferrule 1 has a perfect circular through-hole 2 of xcfx86=0.126 mm which is formed in the longitudinal direction at the center of the column having a length of about 8 mm. A ferrule 1xe2x80x2 shown in (B) of FIG. 1 is a ferrule of the two-core type. The ferrule 1xe2x80x2 is bored with two through-holes 2a, 2b for allowing two optical fibers to pass therethrough.
When the ferrule as shown in (A) of FIG. 1 is produced, the following method has been hitherto adopted. At first, a mixture of zirconia powder and resin is used as a raw material which is molded to have a cylindrical configuration by employing, for example, a mold for injection molding or extrusion molding to mold the cylindrical configuration. Subsequently, a molded product is fired at a temperature of about 500xc2x0 C. to decompose the resin component, followed by being fired at a high temperature of about 1200xc2x0 C. An obtained cylindrical fired product has a through-hole into which a diamond-polishing member having a liner configuration is inserted so that the inner diameter of the through-hole is finely adjusted. Finally, the outer portion of the cylindrical product is machined about the center of the inner hole to finish the ferrule so that it has a perfect circular shape.
In the molding method described above, the fired molded product is slightly contracted due to the firing, and the inner diameter thereof is deviated from a desired dimension. For this reason, the polishing process based on the use of the diamond-polishing member, which is performed after the firing, is a necessary and indispensable treatment. However, the polishing process is laborious, and it requires skill, causing the decrease in productivity. Further, it has been not easy to obtain a perfectly uniform inner diameter concerning the position in the axial direction of the inner hole of the fired product even when the polishing process is performed, for example, because the diamond is not uniformly attached to the linear polishing member. Further, a problem arises in that the equipment cost is expensive, because the diamond-polishing member is consumed and exhausted.
A molding machine and a mold, which are expensive and specialized in this purpose, are required to perform the injection molding or the extrusion molding as described above. Especially, the molding machine and the mold are conspicuously abraded by the extremely hard zirconia powder, and hence their service lives are short as well. It is also possible to use a hard material for the surfaces of the molding machine and the mold. However, the production cost is extremely expensive for such a special molding machine and a special mold. Further, the energy cost is increased, and the energy source is wasted as well, because the firing is performed at a high temperature of 500 to 1200xc2x0 C. in the firing step. If the production cost of the ferrule is increased as described above, the production cost of an optical fiber connector including the ferrule accommodated therein is also increased.
Further, the following problem also arises. Although the ferrule of the one-core type as shown in (A) of FIG. 1 has been hitherto dominantly used, the ferrule of the two-core type as shown in (B) of FIG. 1 or ferrules having more than two cores are gradually demanded. In the case of the ferrules having two or more cores, it is extremely difficult to perform the step to establish the dimension by means of the polishing with the diamond-polishing member. The production of ferrules having three or more cores has been substantially impossible.
When optical fibers are connected to one another by using an optical fiber connector, the process is executed by means of the connection in which tips of the optical fibers are allowed to make mutual abutment, i.e., so-called physical contact (hereinafter referred to as xe2x80x9cPCxe2x80x9d), in order to decrease the reflection loss at the connecting portion. In order to achieve the PC connection, the following processing has been performed. That is, the end surface of the ferrule is polished to have a convex spherical surface or an oblique convex spherical surface, or the end surface of the ferrule is polished to have a flat surface or an oblique flat surface, together with the tip of the optical fiber in a state in which the optical fiber is charged in the ferrule. The conventional ferrule made of zirconia or glass has involved the problem that such process cannot be easily performed.
In the conventional technique, when the ferrule is installed to the optical fiber connector, then the ferrule is installed in a holder, and it is installed to the optical fiber connector together with the holder, in order to adjust the rotational position of the ferrule. A problem has been also pointed out in that the number of parts of the optical fiber connector is increased due to the use of such a holder.
The present invention has been made in consideration of the problems involved in the conventional technique as described above, a first object of which is to provide a ferrule, a method for producing the same, and an apparatus for producing the same, wherein the ferrule can be produced at low energy cost with a simple and cheap equipment without any necessity for the expensive and special equipment such as a molding machine and a mold.
A second object of the present invention is to provide a ferrule, a method for producing the same, and an apparatus for producing the same, wherein the ferrule is excellent in dimensional stability, and it can be produced in accordance with a process with high productivity without necessitating any special skill of an operator.
A third object of the present invention is to provide a ferrule, a method for producing the ferrule, and an apparatus for producing the ferrule, wherein the ferrule can be easily produced even when it is designed to have multiple cores.
A fourth object of the present invention is to provide a ferrule involving an extremely small dimensional error, if any, wherein the ferrule can be easily produced.
A fifth object of the present invention is to provide an optical fiber connector at low cost, which makes it possible to connect optical fibers with high accuracy.
According to a first aspect of the present invention, there is provided a method for producing a ferrule to be used for connecting optical fibers, the method comprising:
depositing a metal by means of electroforming around at least one wire member to produce a rod-shaped electroformed product; and
removing the wire member from the electroformed product.
The method of the present invention is characterized in that the extremely thin wire member is used as a base mold to produce the ferrule in accordance with the electroforming method. The inner diameter of the obtained metal tube is determined by the outer diameter of the wire member. The inner diameter accuracy of the metal tube is also determined by the outer diameter accuracy of the wire member. Therefore, the ferrule, which has the extremely excellent inner diameter accuracy, can be obtained with the wire member which has a cross section (perfect circle) similar to that of the optical fiber, which has a width or a diameter slightly larger than that of the optical fiber, and which has highly accurate linearity and roundness. The obtained ferrule includes an inner hole which has high linearity and roundness. Therefore, it is unnecessary to perform the polishing operation having been hitherto performed to ensure the dimensional accuracy of the inner diameter of the ferrule. In order to remove the wire member from the electroformed product, only the wire member may be dissolved out of the electroformed product, or the wire member is extracted or extruded from the electroformed product, after the metal is deposited around the wire member in accordance with the electroforming. Accordingly, it is possible to obtain the cylindrical metal tube which is formed with the through-hole corresponding to the cross-sectional shape of the wire member. It is desirable that the wire member to be used is a wire member having an outer diameter of not more than 0.2 mm, especially not more than 0.13 mm.
In order to obtain the ferrule by machining the electroformed product, the electroformed product is cut into those having a predetermined length. The outer circumference of the electroformed product may be subjected to cutting about the center of a through-hole which is formed by removing the wire member from the electroformed product.
In the method of the present invention, for example, when the wire member is made of aluminum or alloy thereof, it is preferable that the wire member is removed from the electroformed product by dissolving the wire member with an alkaline or acidic solution after the electroforming. When the wire member is made of iron or alloy thereof, it is preferable that a mold release treatment is applied to the wire member before the electroforming, and the wire member is removed from the electroformed product by extracting or extruding the wire member from the electroformed product after the electroforming.
In the method of the present invention, a two-core ferrule may be produced by arranging two wire members so that they are separated from each other by a predetermined distance to perform the electroforming. In this procedure, the two wire members are arranged so that a pair of pins each having an identical diameter are interposed by the wire members, and thus the spacing distance between the two wire members can be controlled easily and highly accurately. A ferrule having three or more cores can be also produced such that three or more wire members are arranged in parallel to one another while being separated from each other by an identical spacing distance, for example, with two or more pins.
According to a second aspect of the present invention, there is provided a metal ferrule produced in accordance with the method according to the first aspect.
According to a third aspect of the present invention, there is provided a ferrule to be used for connecting optical fibers, the ferrule being formed of only a metal material in an integrated manner.
The metal ferrule of the present invention can be produced, for example, by means of the electroforming method of the present invention extremely accurately, easily, and cheaply. When two optical fibers are joined to one another via an optical fiber connector which accommodates the ferrule, the tip of the ferrule is polished together with the optical fiber for the purpose of flat junction or PC junction. The ferrule of the present invention is polished extremely easily, because it is made of metal. The polishing operation, which is highly accurately controlled, can be applied to the ferrule of the present invention. Therefore, it is possible to perform the PC junction in a well suited manner, and it is possible to join optical fibers with low reflection loss.
The ferrule of the present invention has, at its both ends, holes for allowing the optical fiber to penetrate therethrough, the holes being machined to have a tapered configuration, and it may be used as a sleeve for a mechanical splice.
The ferrule may have a columnar hollow section penetrating in a longitudinal direction of the ferrule, the ferrule may have, at its first end, a first opening which has the same diameter as that of the hollow section, and the ferrule may have, at its second end, a second opening which has a diameter larger than the diameter of the hollow section (see FIG. 20). The hollow section may include a first hollow section, a second hollow section which has a diameter larger than that of the first hollow section, and a third hollow section having a tapered configuration which connects the first hollow section and the second hollow section. In this arrangement, a coated portion of the optical fiber is accommodated in the second hollow section, and a clad of the optical fiber is accommodated in the first hollow section. That is, the second hollow section functions as a conventional ferrule holder. The third hollow section facilitates the introduction of the clad of the optical fiber into the first hollow section.
According to a third aspect of the present invention, there is provided an optical fiber connector for connecting optical fibers, comprising:
a ferrule formed of only a metal material in an integrated manner; and
a housing for accommodating the ferrule.
The polishing process for PC connection can be carried out easily and highly accurately, because the optical fiber connector of the present invention includes the ferrule made of metal. Therefore, it is possible to realize the optical fiber connector with low reflection loss at low cost. The metal ferrule described above is preferably produced by means of the electroforming method according to the present invention.
The housing of the optical fiber connector of the present invention may function as a plug or a jack. The optical fiber connector may further comprise a sleeve for aligning two ferrules. The optical fiber connector may further comprise an adapter for making detachable connection to the plug. In this arrangement, the adapter may include a sleeve for aligning the ferrule at its inside. The optical fiber connector may further comprise an optical fiber cable.
According to a fourth aspect of the present invention, there is provided a wire member-supporting apparatus for being used when a ferrule having multiple cores for connecting optical fibers is produced by means of electroforming, the apparatus comprising:
a base plate;
a pair of first positioning projections provided mutually opposingly on the base plate, each of the first projections having an identical width; and
two wire members stretched in parallel to one another with the pair of first positioning projections interposed therebetween.
The apparatus of the present invention is extremely effective to be used for the production of the ferrule having the multiple cores, the apparatus being installed in an electroforming bath. The two wire members contact with the projections, for example, such that they are urged against the projections such as reference pins provided on the base plate, in mutually opposite directions. Therefore, the wire members are positioned at both sides of the projections respectively. Accordingly, the spacing distance between the two wire members is highly accurately managed in accordance with the diameter of the reference pin. In order to change the spacing distance between a plurality of inner holes formed in the ferrule having the multiple cores, reference pins having a variety of diameters may be previously prepared, and the reference pins may be appropriately exchanged depending on the spacing distance between the inner holes.
The apparatus may further comprise a pair of second positioning projections provided mutually opposingly on the base plate, each of the second projections having an identical width, and two wire members stretched in parallel to one another with the pair of second positioning projections interposed therebetween, wherein the wire members stretched in parallel to one another with the first projections interposed therebetween are mutually parallel to the wire members stretched in parallel to one another with the second projections interposed therebetween, and the respective adjoining wire members are arranged and separated from each other by an identical distance. Accordingly, it is possible to produce a ferrule of the four-core type in which four inner holes are formed and arranged to give an identical spacing distance.